American troops are dying in Afghanistan in record numbers, drone-launched mis-siles are killing more people in Pakistan, American aircraft are carrying out missions over Libya, terrorist detainees are facing military tribunals at Guantanamo Bay, and WikiLeaker Pfc. Bradley Manning is allegedly being tortured. Despite all this grist, the antiwar movement in 2011 is a shadow of its Bush-era self. The obvious explanation for this is that there is a Democrat in the White House, and according to a new study, this simple answer is largely correct.

“The Partisan Dynamics of Contention: Demobilization of the Antiwar Movement in the United States, 2007-2009,” by Michael T. Heaney of the University of Michigan and Fabio Rojas of Indiana University, appeared in the March 2011 edition of the journal Mobilization. The study was based on 5,398 surveys of demonstrators at antiwar protests over three years and numerous interviews with movement leaders. It’s one of the most comprehensive studies undertaken of the contemporary antiwar rabble.

The authors chronicle the collapse of the most visible and romanticized manifestation of antiwar sentiment: the public demonstration. Rallies of hundreds of thousands in 2007 dwindled to the hundreds by the end of 2009. The authors assert it is reasonable to conclude, “the threat to peace from the Obama administration, as perceived by the grassroots constituency of the antiwar movement, must have been very small.” Yet President Obama has a very different approach to war than Sen. Obama did. He effectively broke most of his pledges for peace. The dove turned hawk in mid-flight. “The antiwar movement should have been furious at Obama’s ‘betrayal’ and reinvigorated its protest activity,” the authors write. “Instead, attendance at antiwar rallies declined precipitously and financial resources available to the movement dissipated.”

The difference is that Democrats abandoned the pacifist cause when one of their own decided to use force. Though such social movements routinely claim to be issue-based and nonpartisan, Democrats constituted 54 percent of the hundreds of thousands of antiwar demonstrators in January 2007 and contributed the bulk of the financial support to the umbrella antiwar group United for Peace and Justice. By November 2009, however, with Barack Obama in the White House and (seemingly) firm Democratic majorities in both houses of Congress, the principled antiwar stance collided with political reality, and Democrats dwindled to 19 percent of mere hundreds of activists. The rump movement that remained was financially strapped, fragmented and radicalized.

“While Obama’s election was heralded as a victory for the antiwar movement,” the authors conclude, “Obama’s election, in fact, thwarted the ability of the movement to achieve critical mass.” Those who were the quickest to moralize when George W. Bush was president became masters of compromise under Mr. Obama. At best, they are opportunists, at worst outright hypocrites.

Dedicated peace activists are still out there. Witness the 35 people, including famed Vietnam War-era leaker Daniel Ellsberg, arrested in March outside Marine Corps Base Quantico demonstrating in support of Pfc. Manning. (Their commitment to the cause will be tested with the WikiLeaker taking up residence in the much less accessible Fort Leavenworth, Kan.) Or the Democratic donors who interrupted the president’s Thursday fundraiser with a protest song. Overall, though, those masses who abandoned the barricades after Mr. Obama’s election have demonstrated that they were merely squatters on the moral high ground, exploiting it for partisan gain. The next time these liberals spin a self-righteous narrative of principled opposition to a Republican president, it can be taken with a grain of salt.